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Design >> Analog Design >> What is Diff. Opamp's Av vs. Vod?
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Message started by steven on Feb 17^th, 2006, 12:23pm

Title: What is Diff. Opamp's Av vs. Vod?
Post by steven on Feb 17^th, 2006, 12:23pm

Hi,

I read some differential Opamp designs. One of parameters is open-loop gain Av vs. output swing Vod, which could swing from negative to positive (symmetric to zero). I think the output swing should be symmetric to Vcm, the desired output common voltage which is not zero. How to simulate Av vs. Vod in the case? A sweeping Vcm vs. Av?

Thanks.

Title: Re: What is Diff. Opamp's Av vs. Vod?
Post by raul on Mar 22^nd, 2006, 11:32pm

Vod means output differential voltage which is equal to the difference between the two output terminals of a fully-differential opamp Vod=Vo(+)-Vo(-). The common mode voltage cancels out when you do the substraction. The plot Av vs. Vod probably just shows to you how the voltage gain of the amplifier starts dropping has your output stage starts to clip or to go deep into the linear region. I wouldn't think you would get much information out of a Av vs. Vcm plot because usually you want to select Vcm=Vsupply/2 so that you can obtain the maximum dynamic range at the output of your fully-differential opamp.